Electronic control units are frequently used in dusty, damp, or corrosive surroundings, for example, in automobile construction or in industrial apparatus and machines. In addition, they may sometimes be subjected to mechanical strains, such as impact or shock strains. In order to ensure the function of the included electronic components, the control units are therefore installed in closed housings. The latter must be sealed against the cited damaging influences, however, it is typically necessary to provide pressure equalization openings which permit a gas exchange with the surroundings. In particular, in the event of falling ambient temperature, it must be ensured that water molecules from the air contained in the housing interior may diffuse to the outside in order to avoid harmful condensation in the device.
In order to nonetheless avoid the penetration of liquid water and dust, the gas exchange openings, which are used for pressure equalization and/or vapor pressure equalization, are sometimes closed by gas-permeable membranes. Corresponding membranes may also be provided as self-adhesive labels or parts thereof in order to allow easy attachment. A label of this type is known, for example, from German Published Application DE 196 53 890 A1.
Frequently, however, it is not sufficient to merely cover a gas exchange opening with a membrane, because typical membranes only offer limited protection against the passage of liquids. Thus, for example, water passes through most commercially available membranes if the jet of a high-pressure cleaner is directed thereon. This is not unusual in practice, for example, in control units of construction machinery or electronic devices in industrial technology. Furthermore, exposed membranes may become leaky due to mechanical wear.
Attaching a gas exchange opening, which has a gas membrane stuck over it, in a depression of a housing wall and sticking a protective sticker over the depression is known from WO 99/29150 A 1. The gas exchange remains ensured because recesses are provided in the housing wall, originating from the depression, which are only partially covered by the sticker. However, an arrangement of this type is relatively complex since the depression and recesses must be produced through appropriate shaping and/or machining of the housing wall. In addition, if self-adhesive membranes are used, the problem arises that they may be dispensed into the depression by machines only with difficulty or not at all, so that typically they must be stuck on by hand.